This invention relates to isomerization reactions of fumaronitrile and maleonitrile and particularly to processes for the preparation of maleonitrile.
Maleonitrile and fumaronitrile are useful as intermediates in the production of pharmaceuticals, industrial chemicals and various other useful compounds and as a starting monomer for polymer synthesis. For example, maleonitrile is useful as an intermediate in the preparation of such compounds as pyridoxine and its related compounds, 3- or 5-aminoisoxazoles, nitrogen-containing compounds such as purine and pyrimidine bases.
Various methods exist for the production of maleonitrile and fumaronitrile. U.S. Pat. No. 4,436,671 discloses an improved method of producing unsaturated aliphatic dinitriles such as fumaronitrile and maleonitrile by the ammoxidation of C.sub.4 straight chain hydrocarbons in the presence of a catalyst where the improvement is using a catalyst comprising at least one oxide of vanadium and tungsten, at least one oxide of antimony, phosphorus and boron, and at least one oxide of chromium, nickel, aluminum or silicon. U.S. Pat. No. 3,313,840 discloses a process for the preparation of a mixture of fumaronitrile and maleonitrile by the catalytic dehydrogenation of succinonitrile in the presence of oxygen. Linstead et al., J. Chem. Soc., p. 4839 (1958), disclose a process for the preparation of maleonitrile by the dehydration of amides using phosphorus oxychloride in ethylene dichloride. U.S. Pat. No. 3,959,345 teaches that maleonitrile may be produced by the reaction of hydrogen cyanide with cyanoacetylene.
In addition, approaches for the preparation of maleonitrile include the isomerization of fumaronitrile to yield maleonitrile. For example, U.S. Pat. No. 2,447,810 teaches that fumaronitrile isomerizes to produce maleonitrile when heated with an iodine catalyst. Kruppa et al., Chem. Phys. Lett., 121, 386-389 (1985), and Dalton et al., J. Am. Chem. Soc., 92, 1318-1326 (1970), discuss the photo-initiated isomerization of fumaronitrile to maleonitrile. The isomerization of fumaronitrile to maleonitrile in the presence of butyl lithium in tetrahydrofuran is discussed by Helling et al., Makromol. Chem. 179, 101-108 (1978). It has also been reported that the maleonitrile is isomerized to fumaronitrile by aqueous hydrogen chloride and that it isomerizes spontaneously over a long period of time. Linstead et al., J. Chem. Soc., 4839 (1958).
All of these methods concerning the production or isomerization of maleonitrile and fumaronitrile have some problems. These problems include the formation of various by-products, the difficulty of working on an industrial scale, the necessity of removing and recovering expensive catalysts and little control over whether maleonitrile or fumaronitrile is produced or in what proportions maleonitrile and fumaronitrile are produced. Therefore, what is needed is a simple process for the preparation of maleonitrile or fumaronitrile that uses simple and relatively inexpensive reactants, that produces few by-products, and that can convert fumaronitrile to maleonitrile or vice versa or shift the percentage of maleonitrile present in a mixture of the two.